Gallery theme

I'm using the gallery theme but am a little confused and I'm unable to find any manual, video or forum reference that answers my question.

What is the difference between a gallery page and exhibition and how do they differ from the portfolio. On the demo site there are photos below the slider that appear to be a gallery. I can't figure out what feature adds the photos there. Are they linked to pages or posts? Or drawn from a gallery and where do I set it up?